1. Field of the Invention
The present invention relates to a magnetic contactor having a stationary contact and a movable contact and inserted in a current path, in particular to a magnetic contactor that facilitates extinguishing the arc generated at the time of opening the movable contact from the stationary contact, that is, at the time of current interruption.
2. Description of the Related Art
Magnetic contactors are installed in high voltage direct current power supply circuits for use in electric vehicles, hybrid vehicles and the like. An example of a conventional magnetic contactor, which is a plunger type magnetic contactor disclosed in Patent Document 1, comprises, as shown in FIGS. 9 and 10, a pair of stationary contacts 101 and 102 disposed with a predetermined distance therebetween in a housing 100, movable contacts 103 and 104 disposed opposing the stationary contacts 101 and 102 and allowing closing and opening motion with respect to the stationary contacts, a movable contact holder 105 holding the pair of movable contacts at both ends thereof, and a pair of arc extinguishing means 106 and 107 for extinguishing the arcs that develop in the contact gaps between the pair of stationary contacts 101 and 102 and the pair of movable contacts 103 and 104. Each of the arc extinguishing means 106 and 107 is composed of a pair of permanent magnets with the magnetic pole faces thereof opposing across the contact gap exposing opposite polarities.
The principle of arc extinguishing operation of this conventional example is described in the following with reference to FIGS. 10 through 13. In the current carrying state, the movable contact holder 105 has made the movable contacts 103 and 104 to contact the stationary contacts 101 and 102 to allow an electric current to flow from the stationary contact 101 through the movable contacts 103 and 104 to the stationary contact 102. In the current interruption state, the movable contact holder 105 has been moved upward by solenoid coils (not depicted in the figures) to separate the movable contacts 103 and 104 from the stationary contacts 101 and 102. Turning the current carrying state into the current interruption state generates an arc 108 in the gaps between the stationary contacts 101 and 102 and the movable contacts 103 and 104 as shown in FIG. 11.
The arc extinguishing means 106 and 107 are so arranged that the magnetic flux Φ is generated, as shown in FIG. 12, in the direction orthogonal to the arc 108 and also perpendicular to the page of FIG. 12. The magnetic flux Φ exerts an electromagnetic force, the Lorenz force, on the arc 108 and, as shown in FIG. 12, moves the arc 108 towards the both outer ends in the direction of the arrangement of the stationary contacts 101 and 102 according to the Fleming's left hand rule corresponding to the directions of the magnetic flux and the arc current. Thus, the arcs 108, 108 are extended to the arc extinguishing spaces 109, 109 indicated in FIG. 9 provided in the both end places in the direction of arrangement of the stationary contacts 101 and 102, to be extinguished there.
When the current flows in the reversed direction, that is, from the stationary contact 102 through the movable contacts 104, 103 to the stationary contact 101, as shown in FIG. 13, the arc 108 generated between the stationary contact 101 and the movable contact 103 and the arc 108 generated between the stationary contact 102 and the movable contact 104 are extended inward in the direction of arrangement of the stationary contacts 101 and 102, to be extinguished there.
The current interruption in the conventional example disclosed in Patent Document 1 is performed by increasing the arc voltage beyond the power supply voltage owing to the extended arcs. The arc voltage is determined by the product of the arc electric field and the arc length. Consequently, interruption for a large power supply voltage needs an increased arc electric field or an elongated arc length.
A magnitude of the arc electric field in a gaseous environment is determined by the gas pressure and the type of the gas. The arc electric field can generally be increased by elevating the gas pressure or using a gas exhibiting a large arc electric field such as hydrogen. However, the high gas pressure needs the vessel to be air tight and reinforced, which causes a problem of enlarged vessel. The use of a high arc electric field gas such as hydrogen needs an enlarged gap between contacts in the opened state due to deteriorated breakdown voltage of such a gas, which causes another problem of enlarged solenoid coil for driving the movable contact holder.
Elongation of the arc length, on the other hand, needs to provide such an arc space that ensures a long arc length, which causes a problem of enlarged housing.
In order to cope with these unsolved problems, Patent Document 2 discloses an electromagnetic relay in which a pair of arc extinguishing magnetic bodies is arranged with the opposing faces in different polarity at places of both outside ends of a row of stationary contacts and arc extinguishing spaces are provided for extending the arcs by the Lorenz force produced on the basis of the magnetic flux from the arc extinguishing magnetic bodies in the both sides of each arc extinguishing magnetic body, the both sides positioning in the directions perpendicular to the direction of the row of stationary contacts and also perpendicular to the direction of the open/close movement of the stationary and movable contacts.
[Patent Document 1]
Japanese Unexamined Patent Application Publication No. H07-235248
Japanese Unexamined Patent Application Publication No. 2008-226547
The conventional example disclosed in Patent Document 2 still has a problem of elongated dimension in the direction of arrangement of the stationary contacts because the arc extinguishing magnetic bodies are disposed at the places of both outside ends of the row of stationary contacts. The electromagnetic relay of Patent Document 2 avoids the interference between arcs regardless of the current flow direction because arc extinguishing spaces are disposed at the both sides of the arc extinguishing magnetic body in the direction perpendicular to arrangement of the stationary contacts. In the configuration of this conventional example, however, the width in the direction perpendicular to arrangement of stationary contacts must be elongated in order to ensure necessary arc length for extending the arc to interrupt a high power supply voltage. Thus, this conventional example too, does not meet the requirement for size reduction of a magnetic contactor, leaving an unsolved problem.